1. Field of the Invention
The present invention relates to cryogenic coolers. More specifically, the present invention relates to methods and apparatus for Split-Stirling cryogenic coolers having multiple expander elements operating from a single compressor.
While the present invention is described herein with reference to illustrative embodiments for particular applications, it should be understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications, and embodiments within the scope thereof and additional fields in which the present invention would be of significant utility.
2. Description of the Related Art
In many applications, there is a need for a small, lightweight cooling system. Consider, for example, the fact that a single conventional infrared detector is typically packaged and positioned to permit reception of infrared radiation from a single field-of-view. In order to expand the view window, multiple infrared detectors must be utilized, for example, by placing one detector in each quadrant. However, each of the four detectors must be cooled to function properly. Generally, in order to cool four infrared detectors, four separate cryogenic cooler systems have typically been required, each having an associated compressor and expander.
The Stirling cycle engine consists of a compressor piston with a cylinder, an expansion piston with a cylinder, and a drive mechanism. The drive mechanism converted the rotary motion of a motor and crankshaft to a reciprocating motion of the two pistons ninety degrees out-of-phase. A regenerator and a crankcase housing were also included. Cooling is effected by the expansion cycle of a gas at the regenerator/expander assembly.
The basic Stirling cycle engine technology is employed in a Split-Stirling cooler with the exception that the reciprocating displacer piston and cylinder located within the expander are physically separated from the compressor and the regenerator is located within the displacer piston. The reciprocating displacer piston within the expander and the compressor are then interconnected with a small diameter gas transfer line which is sufficiently flexible to avoid the introduction of excessive spring torque to the system. This design permits the compressor, which is large compared to the expander, to be located remotely where available volume and heat rejection capability exists. The Split-Stirling cryogenic cooler is pneumatically driven so that gas pressure differentials on opposite sides of the displacer piston and cylinder provide the motive force to the cryogenic cooler.
While the Split-Stirling cycle engine is generally smaller and lighter than the Stirling cycle cooler, unfortunately, the use of conventional Split-Stirling cycle engines, provides a design which is too heavy, bulky and power hungry for many applications. Thus, a need remains in the art for a small, lightweight, low power cryogenic cooling system.